Post-deflected color kinescope



POST- 2 SHEETS-SHEET 1 Filed Sept. 14, 1950 lea IN VENTOR ATTQ R N EY Nov. 25, 1952 J. A. RAJCHMAAI I 2,6 9,608 I POST-DEFLECTED COLOR KINESCOPE Filed se t. 14, 1950 2 SHEETS'-SHEET 2 INVENTOR I ATTORN EY Patented Nov. 25, 1952 POST-DEFLECTED COLOR. KINESCOPE Jan A. Rajchman, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application September 14, 1950, Serial No. 184,857

8 Claims.

This invention relates to cathode-ray tubes and particularly to improvements in colorkinescopes of the kind wherein the scanning beam, or electrons derived from said'beam, are post-deflected (i. e. deflected, focused or otherwise directed subsequent to the scanning movement) for the purpose of selectively activating the different color-phosphors on the target surface of a screen.

Those skilled in the art to which this invention appertains know that color-kinescopes of the post deflected variety possess certain advantages over color-television tubes of the presently popular directional-screen variety. By way of example; directional-screen kinescopes must employ either a rotating beam or an assembly of three-guns for selectively activating the difierently colored-phosphor screen-areas, but post-deflected tubes may, and usually do, employ a single-gun and a conventional (horizontal and vertical) scanning pattern. Thus, tubes of the latter type have no beam-convergence problems, either of a mechanical or electrical nature. Furthermore, post-deflected tubes use substantially lower scanning voltages, hence their auxiliary circuits present no complex problems of insulation or design.

Post-deflected kinescopes are of two kinds (1) the kind wherein the post-deflected electrons are derived directly from the primary-beam and (2) the kind wherein the electrons that are post-deflected are secondary-electrons, derived from impact of the primary beam upon a thin-metal target mounted in front of the electron-sensitive surface of the screen.

Copending application of Rajchman, Serial No. 151,397 filed March 23, 1950 describes a postdeflected color-kinescope of the first mentioned variety and copending application of Rosenberg and Rajchman Serial No. 168,562 filed June, 16,

1950 describes a color kinescope of the latter (secondary-electron) variety.

The color-kinescopes described by Rajchman and by Rajchman and Rosenberg, in their above identified disclosures, possess all of the advantages peculiar to post-deflected tubes. However, the tubes there described may be said to be more complex and costly than is desirable in an instrument designed for use in the home; The principal complexity is the target or screen assembly which, in the case of a tri-color tube, comprises not less than six separate plate-like elements.

Accordingly, the principal object of the present invention is to provide an improved kinescope of 2 the post-deflected type and one characterized by the simplicity and economy of its parts.

Another and important object of the invention is to provide a post-deflected color-kinescope wherein, if desired, color-selection may be determined by the instantaneous potential of the cathode and the intensity of the selected color may be determined, simply by modulating the cathode-grid potential of the gun of the tube with video-signals transmitted by any known type (e. g. dot-sequential, line-sequential or field sequential) television-system.

The foregoing and other objects are achieved in accordance with the invention by the provision of a tri-part target assembly comprising (1) a color-screen wherein the sub-elemental color-phosphor areas .are concentrically arranged, (2) a masking electrode for deriving one or more annular beams of electrons from the normally solid scanning beam and (3) an electron-lens element capable of altering the inner and outer diametrical dimensions of the annular beam or beams and causing the beam electrons to activate the concentrically disposed sub-elemental phosphor covered areas on the screen in the manner and sequence dictated by the video signals.

The invention is described in greater detail in connection with the accompanying two sheets of drawings, wherein:

Fig. 1 shows a post-deflection color-kinescope, embodying the invention, and appropriate circuit connections for its various electrodes;

Fig. 2 is fragmentary plan view of the apertured masking element of the target-assembly of the kinescope of Fig. 1;

Fig. 3 is a similar View of the color-screen element of the target-assembly and;

Fig. 4 is a vertical sectional view of the tripart target assembly, the drawing being marked to indicate the manner in which the mask and lens elements of the target-assembly cooperate in directing the beam, selectively, to the several differently colored-phosphor parts of the raysensitive areas on the target surface of the screen.

The color-kinescope shown in Fig. 1 comprises an evacuated envolope having a neck portion I and a bulbous portion or main chamber 3, the latter being provided with a transparent or translucent window 5 through which the obverse face is of the screen 1 of the tri-part color-target assembly (1, 9, H) of the invention may be viewed. The single electron-gun in the neck of the tube may be of conventional form and di- 2,e19,eos

mensions and, in the instant case, comprises an indirectly-heated cathode 155, a control grid i5, a screen or accelerating electrode I7 and first and second anodes l9 and ill respectively. The second anode 21 comprises a conductive coating which covers the inner surface of the envelope from a point adjacent the leading end of the first anode iii to point just short of the innermost plate ll of the target assembly. This anode 2i serves to accelerate the beam 13 and, further, to establish an electron lens-field (indicated by the curved lines L) which operates to bend or normalize the beam so that it always approaches the target element l I at an angle of substantially 90. A conventional coil assembly or yoke 23, mounted on the neck of the tube, is here employed to impart the requisite horizontal and vertical components of the scanning movement to the beam.

The part I! of the target assembly l, 9, ll, upon which the scanning beam B first impinges comprises a thin yet rigid metal (e. g. nickel) plate containing a multiplicity of ring-shape holes 25, the centers of which are masked by little discs 2?, supported by two or more very thin supporting arms 29. of the holes 25 and the discs 2? operate to convert the normally solid scanning beam B into one or more hollow beams B (Fig. 4) of annular cross-section. The distance between the centers of the discs 2'? in the masking plate ii is preferably smaller than the diameter of the solid beam B, hence said beam, at any given instant, will be broken up into more than one hollow annular beam B in passing through the apertures in the plate i i. (In order to simplify the drawing, but one such hollow beam B is shown, in Fig. 4).

The second element of the tri-part target assembly is an electron-lens element in the form of a flat metal plate 9 containing the same number of circular holes 3| as there are ring-shape holes 25 in the mask l i. The center of each circular hole 3! in the plate 9 is in register with the center of the disc 2? of one of the ring-shape mask-holes 25. The diameter of each or said circular holes 3! is equal to or slightly greater than the outer diameter of the ring-shape hole with which it is paired. The beam-focusing plate or lens element 9 is mounted parallel to the beamforming accelerating plate or mask ii at a distance of from to 1.5 times the diameter of its holes. It is electrically insulated from the mask II and, as indicated in Fig. l, is ordinarily operated at a potential of volts with respect to the cathode l3 and has, therefore, a retarding effect on the electrons.

The screen element 7, upon which the electrons eventually impinge, comprises a foundation member If constituted of glass or other transparent or translucent material. The inner or target surface of this plate-like foundation member is provided with a light-transparent, electrically conductive coating or layer To (see Fig. l). The outer surface of this conductive layer l'c contains a multiplicity of ray sensitive areas 'Ea of elemental image-dimensions, disposed in register with the similarly dimensioned holes 25 and iii in the mask H and focusing plate Each of these elemental ray-sensitive areas la comprises a number (in this case, three) of concentrically disposed ray translating parts lg, ET and lb or" sub-elemental image-dimensions, (as that term is understood in the television art).

The arcuate segments Each sub- 4 elemental part or area is constituted essentially of a fluorescent material capable of emitting light of a color individual to that part. The outer or target surface of these fluorescent (phosphor) deposits may support an electron-transparent conductive layer id, e. g. of aluminum, applied by an evaporation process, in vacuo. If such a film id is employed it is electrically connected to the other metallic coating 10.

The colored lights emitted by different colorphosphors may be, and usually are, of different intensities, per unit area. It is usually desirable that each of the sub-elemental areas lb, ir and lg emit the same quantity of light when struck by the same number of electrons of the same velocity. Accordingly, in order to compensate for the differences in the sizes of the circular phosphor-parts 'ig, VT and lb, the smallest or innermost circle lg is preferably constituted of the phosphor which exhibits the maximum relative intensity of emission, and the larger circles 11 and 'lb comprise phosphor materials of respectively lower intensities of emission. The particular phosphor materials employed may be the ones specified in Leverenz U. S. Patent 2,310,- 863 in which case the green phosphor (zinc silicate with manganese activator) comprises the innermost ring lg, the red phosphor (cadmium borate with manganese activator) the central ring 77' and the blue phosphor (calcium manganese silicate with titanium activator) the outermost ring lb.

The deposition of these cliiferent color-phosphors on the conductive surface 'lc of the screen i may be accomplished with the aid of suitable stencils (not shown) either by deposition in a settling tank (not shown) or by the silk-screen method. In either event, three different stenoils (not shown) are used. In depositing the inner phosphor part 7 g, a metal stencil or a silkscreen with circular phosphor-pervious apertures may be used. If the silk-screen method is employed the other two screens have annular phosphor-pervious apertures of dimensions corresponding to those of the blue and red areas, it and 71', respectively. If metal stencils are used, the second and third stencils are provided with appropriately dimensioned ring-shape apertures with their centers supported by two or more Very thin supporting arms, as in the case of the mask H, previously described. The masking electrode H, the focusing plate 9, and the metal or cloth stencils used in laying down the discrete phosphor areas lb, 7r, lg on the foundation of the screen i, may be made by the photoengraving technique heretofore used (see copending application of H. B. Law, Serial No. 158,901) in making the masking plates of so-called maskedtarget kinescopes.

The operation of the color-kinescope of the invention is as follows: The normally solid beam B from the electron-gun in scanning the target surface of the mask ll, encounters the ring-shape holes 25 in the mask ll which divide the beam into a plurality of sub-beams or jets B (Fig. 4) of annular cross-section. These hollow jets pass through the circular holes 3| in the plate-like electron-lens element 9. This plate 9 is operated at potentials considerably lower than that of the mask H and screen 7. As a consequence, electrostatic lens-fields are formed adiacent to the apertures 31 in the lens plate 9. Each lens-field operate to alter the (inner and cuter) diametrical dimensions of the particular hollow jet of electrons B that passes through that field. After passing through the lens-plate 9 the beam is post-accelerated by the reason of the high voltage applied to the metal layer 10 (or layers 10 and 1d) on the screen I. Appropriate operating voltages for the mask (e. g. 8 kilovolts) and screen (e. g. 20 kilovolts) are marked on Fig. 1 of the drawing.

During the scanning movement a hollow jet of electrons bombards one or another of the concentrically disposed sub-elemental phosphor parts 1g, 71* or lb of each ray-sensitive elemental area la on the target surface of the screen I. The particular sub-elemental phosphor area upon which the electrons impinge at any given instant depends either (a) upon the strength of the electrostatic lens-field through which the hollow beam or jet B passes or (b) the velocity of the electrons passing through said field. The strength of the lens-field depends upon the instantaneous potential of the lens-plate 9 with respect to the cathode l3 and this potential is determined by the color keying signals. As shown by the brokenlines Bb in Fig. 4, when the beam retains the annular dimensions with which it was endowed in passing through the masking plate 9 it will strike only the outer (blue) phosphor ring ID on the screen I. When the lens field is intensifled to a certain degree the diametrical dimensions of the annular beam B are reduced, as indicated by the broken lines Br, and it strikes only the intermediate (red) phosphor ring 11'. A greater intensification of the field about the apertures in the lens plate 9 concentrates the beam and focuses it, as indicated by the solid lines Bg, upon the innermost (green) phosphor 7g. If the lens-plate 9 is caused to operate at potentials close to cathode-potential a very sensitive control is achieved.

Color-kinescopes constructed in accordance with the principle of the present invention are susceptible of more than one mode of operation and it is apparent that various circuit arrangements may be devised for each mode. One way of operating a post-deflected kinescope is to apply the color-selecting keying impulses directly to the lens-plate and to vary the cathode-grid potential with the video signals. As a practical matter the interelectrode capacitance of the tripart target assembly 1, 9, I I may limit this method to the (relatively low) keying speeds used in field-sequential and line-sequential television systems.

A circuit that avoids the above mentioned limitation is shown in Fig. 1. Here the color-keying voltages are applied directly to the cathode l3 from a cathode-follower tube 33. At the same time, keying-signals of opposite polarity are taken off the plate 35 of the follower tube 33 and applied to the grid 3! of a double triode 39. The plate or plates 4| of the double diode 39 are connected through a capacitor 43 or to the control grid E5 of the kinescope. Therefore, when the resistor A5 in the cathode follower circuit, and the degenerative resistors 41 and plate resistor 48 of the double triode 39 are properly adjusted, the potential on the grid I5 of the kinescope varies identically with the potential of the oathode I3. Since the potential on the lens plate 9 is fixed, the keying pulses on the cathode l3 determine the difference in potenital of the lens plate with respect to the cathode and hence the particular color upon which the annular beam impinges. The lens-effect of the tri-part screen assembly is varied in this case by varying the velocity of the electrons which pass therethrough,

rather than varying the contour of the lens-field about each hole (as would be the case if the keying signals were to be applied to the lens plate).

In order to prevent the keying voltages on the cathode 13 from altering the focus of the-beam, the accelerating electrode l1 and the first anode I9 are A.-C. connected to the cathode l3 through large capacitors 49 and 5!, and are D.-C. connected to the voltage source 53 through suitable inductors or choke coils 55 and 57. In order to vary the intensity of the beam in accordance with the incoming video signals, said signals are applied to the grid 59 of the other half of the double triode and, since the plates 41 of this tube are connected to the grid E5 of the kinescope, the video signals operate to vary the intensity of the beam B in accordance with said signals. When the keying voltages are applied to the cathode iii of the kinescope slight changes in the position of the beam may occur. However, such changes are insignificant because the percentage variation in velocity of the electrons in the region in which they are deflected is quite small.

From the foregoing it will be apparent that the present invention provides an improved kinescope of the post-deflected variety and one characterized by the simplicity and economy of its parts.

What is claimed is:

l. A television screen comprising a foundation member having a target surface containing a multiplicity of spaced apart electron sensitive areas consisting essentially of a plurality of concentrically disposed electron-sensitive parts.

2. The invention as set forth in claim 1 and wherein said concentrically disposed electronsensitive parts of said target surface are each constituted essentially of a fluorescent material capable of emitting light of a color individual to that part.

3. The invention as set forth in claim 2 and wherein the fluorescent materials of which said different fluorescent materials normally emit colored light of respectively different intensities, per unit of area, and wherein the innermost one of said concentrically disposed electron-sensitive parts comprises the fluorescent material of the relative maximum intensity of emission.

4. A television image-screen comprising a foundation member having a target surface containing a multiplicity of spaced apart electron-sensitive areas of elemental image-dimensions, said raysensitive areas each comprising a plurality of concentrically disposed electron-sensitive parts of sub-elemental image-dimensions.

5. In an electron-beam tube, electrode means for producing an electron-beam of substantially annular cross-section, a screen mounted in spaced relation with respect to said electrode means and comprising a target surface having a plurality of concentrically disposed electron-sensitive parts disposed in the path of said annular beam, and an electron-lens element mounted adjacent to the space between said electrode means and screen for altering the diametrical dimensions of said annular beam whereby selectively to activate said concentrically disposed electron-sensitive parts of said target surface.

6. The invention as set forth in claim 5 and wherein said electron-lens element comprises a metal plat containing apertures of a diameter sufficient to permit the passage of said annular beam, the centers of said apertures being disposed in register with the common center of said concentrically disposed electron-sensitive parts of said screen.

{7;Th invention as set forth in claim 5 and wherein said annuiar-beam producing means comprises an electron-gun and a mask mounted in the path of the electrons from said gun, said mask-comprisinga diaphragm containing a multiplicity of electron-opaque portions each substantially surrounded by a plurality of circularly gun is mounted remote from said mask in a positionto scan said target surface.

JAN A. 'RAJCHMAN.

8 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Herbst June 16, 1942 Szikiai Feb. 22, 1949 Chiiowsky Jan. 31, 1950 

